1. Field of the Invention
The present invention relates to adhesive tapes, more particularly to tapes that can be firmly adhered to a substrate and can be removed without damaging the substrate.
2. Discussion of the Art
Adhesive tapes, such as, for example, pressure-sensitive adhesive tapes, are usually firmly bonded to substrates because subsequent separation of the tapes from the substrates is neither intended nor desired. However, there are adhesive tapes wherein the adhesives are specifically formulated to allow clean and easy removal from substrates after use, such as, for example, the adhesive used for "Post-It" brand removable notes. These adhesives usually do not exhibit a substantial level of holding power, e.g., greater than 4 to 6 oz./in. adhesion to standard copy paper. Adhesives formulated to provide a substantial level of adhesion, e.g., greater than 30 oz./in. adhesion to paper, are generally difficult to remove without damaging the substrate.
U.S. Pat. No. 4,024,312 discloses a film backed, normally tacky and pressure-sensitive adhesive tape which is highly extensible and highly elastic. The tape can be easily removed from a surface to which it has been applied by stretching it lengthwise in a direction substantially parallel to the plane of the surface. The film backing is formed from a composition comprising elastomeric and thermoplastic A-B-A block copolymers, and possesses a lengthwise elongation to break of at least about 200%, preferably at least about 300%, and a 50% rubber modulus of not above about 2,000 lbs/sq. inch. This low rubber modulus is stated to be an important factor in insuring easy stretchability and easy removal of the tape at high elongations. The elasticity of the backing is important for conformability and other purposes and the elastic recovery from 50% stretch is preferably at least about 75%, more preferably at least about 90%. A preferred use for this tape is the so-called "ouchless" bandage. German (OS) 3331 016 A1 discloses another adhesive tape for removable adhesive bonds, whereby the tape exhibits high elasticity and low plasticity. The adhesive strength is less than the cohesive strength, and the adhesion capability essentially disappears as the film is being stretched. The ratio of peel force to tear strength of the tape is about 1:2 or greater and the adhesive bond can be released by pulling the film in the direction of the plane of the adhesive joint. The tape is used as a load-resistant adhesive to bond to rigid solid substrates. A separation of the adhesively bonded materials is possible without damage to the substrate.
Both of these tapes are highly elastic and exhibit large recoil when the stretching force is removed, in the same way a rubber band snaps back upon removal of the stretching force. This recoil characteristic can be dangerous, and increases the force required to debond these tapes at low angles. Finally, these highly elastic tapes tend to substantially recover their original shape when the stretching force is removed, and they are therefore not useful for indication of tampering or for guaranteeing single uses for hygienic purposes.